In order to make it easy for a passenger to get on to or off from a rear seat (i.e. walk-in operation), it is known to turn down a seatback of a front seat in a vehicle forward direction for the purposes of canceling a locked state (i.e. engaging state) of an upper rail for supporting the seat relative to a lower rail fixed to a vehicle seat, and then to move the front seat in the forward direction. In addition, an original position of the seat is stored (memory function) so that the seat can be returned to that position after the passenger gets on to or off from the rear seat. Such seat sliding device for a vehicle is disclosed in U.S. Pat. No. 5,688,026 and U.S. Pat. No. 6,227,596.
According to the seat sliding device disclosed in the above publications, the seat returns to the stored original position, i.e. where a memory retaining runner is locked (i.e. engages) relative to the lower rail, with the seatback being turned down after the passenger gets on to or off from the rear seat. Then, the slide operation of the upper rail relative to the lower rail is prohibited when the seatback is turned up. The seat can be locked in a forward position relative to the position of the memory retaining runner. In this case, the engagement of the memory retaining runner relative to the lower rail is released through the normal operation of the seat afterwards.
When the seatback is turned up in the forward position relative to the memory retaining runner, the seat is prohibited to move. That is, the sliding operation of the seat is restricted. In this state, a sufficient space is not provided in front of the seat for the passenger to access the seat. Thus, the sliding operation of the seat should be permitted by operating an operation handle so that the seat is moved to a position with which the passenger can get onto the seat.
In addition, according to the seat sliding device disclosed in the above publications, the seatback can be turned up in the forward position relative to the position of the memory retaining runner where the locked state of the sliding operation of the seat is obtained so that the memory of the seat position can be deleted. At this time, if the memory retaining runner disengages rapidly from the, lower rail in case of the normal operation of the seat even if the engagement of the memory retaining runner with the lower rail is not strong, a lock mechanism of the memory retaining runner may be damaged. Further, since a large force is added to the memory retaining runner by a rearward movement of the seat, the memory retaining runner and the memory lock mechanism may be damaged and malfunction.